Electric power tool including a plurality of circuit boards

ABSTRACT

An electric power tool, which uses a DC brushless motor as a drive source and controls the DC brushless motor by a switching element, can include a tubular housing main body portion accommodating the DC brushless motor, and a grip portion protruding from a side portion of the housing main body portion. The switching element is arranged inside the grip portion, and is spaced apart from an electronic circuit board for an electronic component for operating the switching element.

This is a Divisional of application Ser. No. 13/121,114 filed Apr. 13,2011, which is a National Stage of Application No. PCT/JP2009/062090filed Jul. 2, 2009. The prior applications, including thespecifications, drawings and abstracts are incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electric power tool that uses a DCbrushless motor as the drive source and controls the DC brushless motorby a switching element.

2. Description of the Related Art

In an electric power tool that controls a DC brushless motor byutilizing a switching element, it is common practice to arrange theswitching element behind the DC brushless motor. However, arrangement ofthe switching element behind the DC brushless motor involves an increasein the entire length of the electric power tool, resulting indeterioration in the usability of the electric power tool.

To solve this problem, Japanese Laid-Open Patent Publication No.2007-283447 discloses an electric power tool in which a switchingelement is mounted to an electric circuit board together with anelectronic component and is arranged at a protruding end of a gripportion. As a result, there is no need for providing a space for theswitching element behind the DC brushless motor, making it possible tomake the entire length of the electric power tool relatively small.

However, in the electric power tool disclosed in Japanese Laid-OpenPatent Publication No. 2007-283447, the switching element and theelectronic component such as a microprocessor for operating theswitching element are mounted to the same electric circuit board, sothat measures must be taken for protection against heat so that theelectronic component may not be affected by the heat of the switchingelement.

Therefore, there is a need for the switching element to be spaced apartfrom the electronic component such as a microprocessor without involvingan increase in the entire length of the electric power tool, therebyrelieving the need for taking measures to protect the electroniccomponent from heating.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is providedan electric power tool that uses a DC brushless motor as a drive sourceand controls the DC brushless motor by a switching element, comprising atubular housing main body portion accommodating the DC brushless motor,and a grip portion protruding from a side portion of the housing mainbody portion, wherein the switching element is arranged inside the gripportion, and is spaced apart from an electronic circuit board for anelectronic component for operating the switching element.

According to the first aspect of the present invention, the switchingelement is arranged inside the grip portion, and is spaced apart fromthe electronic circuit board for the electronic component for operatingthe switching element. As a result, the heat of the switching element isnot easily conducted to the electronic component, making it possible toreduce the measures for protecting the electronic component fromheating.

Further, since the switching element is arranged inside the gripportion, there is no need to provide a space for the switching elementbehind the DC brushless motor, thereby preventing an increase in theentire length of the electric power tool.

According to a second aspect of the present invention, there is formedat a protruding end of the grip portion a battery pack connectionportion to which a battery pack is detachably connected, with theelectronic circuit board for the electronic component being arrangedinside the space of the grip portion and along the battery packconnection portion.

According to another aspect of the present invention, the switchingelement is mounted to a power circuit board, and the power circuit boardis set in position along the longitudinal direction of the grip portion,with the board surface thereof being oriented substantially in the samedirection as the board surface of a motor board attached to an endsurface of the DC brushless motor, wherein both end edges in the widthdirection of the power circuit board are supported by an inner wallsurface of the grip portion.

According to the present invention, both end edges of the power circuitboard to which the switching element is attached are supported by theinner wall surface of the grip portion. As a result, the contact areabetween the power circuit board and the grip portion can be reduced,making it limited for the heat of the switching element to be conductedto the grip portion.

Further, since the board surface of the power circuit board is orientedsubstantially in the same direction as the board surface of the motorboard attached to an end surface of the DC brushless motor, no twistingis generated in a plurality of power lines connecting the power circuitboard (the switching element) and the motor board (the DC brushlessmotor), thereby making the wiring space to be compact.

According to another aspect of the present invention, the switchingelement is covered with a heat radiation material or a heat insulationmaterial.

As a result, the heat of the switching element is not easily conductedto the grip portion.

According to another aspect of the present invention, the inner wallsurface of the grip portion is covered with a heat radiation material ora heat insulation material.

As a result, the heat of the switching element is not easily conductedto the grip portion.

According to the present invention, the switching element is arrangedinside the grip portion so as to be spaced apart from an electroniccomponent such as a microprocessor, whereby it is possible to reduce theheat protection measures for the electronic component without involvingan increase in the entire length of the electric power tool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of an electric power toolaccording to an embodiment 1 of the present invention.

FIG. 2 is a diagram showing a drive circuit configuration of a DCbrushless motor.

FIG. 3 is a rear view of a motor board for the DC brushless motor and ofa power circuit board.

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1

In the following, an electric power tool according to an embodiment 1 ofthe present invention will be described with reference to FIGS. 1 to 3.The electric power tool of this embodiment is a rotary driving tool (animpact driver) using a DC brushless motor as the drive source.

<Outline of Electric Power Tool>

As shown in FIG. 1, a housing 11 of an electric power tool 10 accordingto this embodiment includes a housing main body portion 12, and a gripportion 15 formed to protrude from a side portion (the lower portion asseen in FIG. 1) of the housing main body portion 12. The grip portion 15includes a handle portion 15 h grasped by the user when he or she usesthe electric power tool 10, and an exposed portion 15 p located on theprotruding end (lower end) side of the handle portion 15 h. The handleportion 15 h is formed in a relatively small diameter so that it can beeasily grasped by the user. And, at a proximal end portion of the handleportion 15 h, there is provided a trigger type switch lever 15 r to bepulled by the user with a finger.

The exposed portion 15 p of the grip portion 15 expands in a directionnearly perpendicular to the longitudinal direction with respect to thehandle portion 15 h, and, under the exposed portion 15 p, there isprovided a battery pack connection portion 16 to which a battery pack(not shown) is connected.

A DC brushless motor 20, a planetary gear mechanism 24, a spindle 25, adriving force generation mechanism 26, and an anvil 27 in that orderfrom the rear side are coaxially accommodated in the housing main bodyportion 12. And, the rotational power of the DC brushless motor 20 istransmitted to the spindle 25 via the planetary gear mechanism 24, andthe rotational force of the spindle 25 is converted to a rotationaldriving force by the driving force generation mechanism 26, and istransmitted to the anvil 27. The anvil 27 is supported by a bearing 12j, provided at the forward end of the housing main body portion 12, soas to be rotatable around the axis and to be incapable of displacementin the axial direction. A chuck portion 27 t for the attachment of adriver bit, socket bit or the like (not shown) is provided at theforward end portion of the anvil 27.

<DC Brushless Motor 20>

As shown in FIG. 1, the DC brushless motor 20 includes a rotor 22provided with a permanent magnet, and a stator 23 provided with a drivecoil 23 c. The stator 23 is provided with a tubular body portion (notshown) and six tooth portions 23 p protruding radially inwards from theinner peripheral surface of the tubular body portion, with the toothportions 23 p being arranged at equal intervals around the rotor 22. Thedrive coil 23 c is wound around each tooth portion 23 p through theintermediation of an insulation material.

Further, magnetic sensors 32 for detecting the position of a magneticpole of the rotor 22 are mounted to the rear end portion of the stator23 via a motor board 33 (described below). As a result, by sequentiallysupplying current to each drive coil 23 c from a drive circuit 40 whiledetecting the position of the magnetic pole of the rotor 22 by themagnetic sensor 32, it is possible to rotate the rotor 22.

<Magnetic Sensor 32>

Three magnetic sensors 32 are used as a set, with the three magneticsensors 32 being arranged at equal intervals in the peripheraldirection. The three magnetic sensors 32 are mounted to a ring-likemotor board 33 shown in FIG. 3. The motor board 33 is fastened by ascrew to the rear end portion of the stator 23 while being coaxial withthe stator 23 of the DC brushless motor 20 (See FIG. 1).

Further, a relay portion T (See FIG. 3) connecting the windings of thedrive coils 23 c and power lines 41 (described below) is provided on themotor board 33.

<Drive Circuit 40>

As shown in FIG. 2, the drive circuit 40 of the DC brushless motor 20 isprovided with a power source circuit portion 42, a three-phase bridgecircuit portion 45 including six switching elements 44, and a controlcircuit portion 46 for controlling the switching elements 44 of thethree-phase bridge circuit portion 45. The power source circuit portion42 is for receiving an electric power supplied to the electric powertool 10 from a battery 42 in the battery pack via terminals 42 t of thebattery pack connection portion 16. The power source circuit portion 42is provided with a power source line 42 c connected to the terminals 42t, a power source smoothing capacitor 43 c, and a shunt resistor 43 sfor current detection connected in series to the power source line 42 c.

The three-phase bridge circuit portion 45 is connected to the powersource line 42 c in parallel with the power source smoothing capacitor43 c, and the three output lines 41 (hereinafter termed the power lines41) of the three-phase circuit portion 45 are connected to the windingsof the drive coils 23 c via the relay portion T of the motor board 33,as described above. Here, there are used, for example, field-effecttransistors (FET) as the switching elements 44 of the three-phase bridgecircuit portion 45.

The control circuit portion 46 includes an electronic component such asa microprocessor, IC or the like for operating the switching elements44. The control circuit portion 46 receives signals from the threemagnetic sensors 32, and, based on the signals, an on/off-control of theswitching elements 44 constituting the three-phase circuit portion 45 isperformed (Refer to the hollow arrow in the diagram). As a result, it ispossible to sequentially supply current to the drive coils 23 c of thestator 23.

Further, signals from various switches 46 a and 46 b for switchingtightening speed and for turning on/off a tool light are input to thecontrol circuit portion 46. Further, LEDs 46 x and 46 y indicatingtightening speed, battery capacity, etc are incorporated into thecontrol circuit portion 46.

The drive circuit 40 of the DC brushless motor 20 is set inside the gripportion 15 in the form of an electronic circuit board 50 and powercircuit board 60.

<Electronic Circuit Board 50>

The electronic circuit board 50 is the board to which the controlcircuit portion 46, the various switches 46 a and 46 b, and the LEDs 46x and 46 y are attached. As shown in FIG. 1, the electronic circuitboard 50 is mounted inside the exposed portion 15 p of the grip portion15 while lying along the upper surface of the battery pack connectionportion 16.

Here, on the front portion surface of the exposed portion 15 p of thegrip portion 15, there are provided an operating portion (not shown) foroperating the various switches 46 a and 46 b, and a display-checkingportion (e.g. a transparent portion) allowing a user to check a displayof the various LEDs 46 x and 46 y.

<Power Circuit Board 60>

The power circuit board 60 is a board to which the six switchingelements 55 constituting the three-phase bridge circuit portion 45, thepower source smoothing capacitor 43 c of the power source circuitportion 42, and the shunt resistor 43 s, etc. are mounted. As shown inFIG. 1, the power circuit board 60 is set standing within the handleportion 15 h of the grip portion 15 (i.e., extending along thelongitudinal direction of the handle portion 15 h), with the boardsurface thereof being oriented to the front side of the electric powertool 10 in the same way as the board of the motor board 33. And, boththe right and left end edges of the power circuit board 60 are supportedby the inner wall surface of the handle portion 15 h of the grip portion15.

Three switching elements 44 are mounted to the front surface of theboard of the power circuit board 60 so as to be arranged vertically atpredetermined intervals, and the power source smoothing capacitor 43 cis arranged on the lower portion of the front side of the board.Similarly, as shown in FIG. 3, three switching elements 44 a are mountedto the rear surface of the board of the power circuit board 60 so as tobe arranged vertically at predetermined intervals, and the shuntresistor 43 s is arranged on the lower portion of the rear surface ofthe board. Further, as shown in FIG. 1, the surfaces of the switchingelements 44 mounted to the board front surface and the board rearsurface of the power circuit board 60 are covered with a heatsink 65formed of aluminum alloy.

The power circuit board 60 and the electronic circuit board 50 areelectrically connected to each other by a flexible control cable 62.

Further, as shown in FIG. 3, one ends of power source lines 42 c of thedrive circuit 40 are connected to the power circuit board 60, and theother ends of the power source lines 42 c are connected to the terminals42 t of the battery pack portion 16 as shown in FIG. 2. Further, asshown in FIG. 3, the power circuit board 60 and the relay portion T ofthe motor board 33 are connected to each other by three power lines 41.Here, the respective board surfaces of the power circuit board 60 andthe motor board 33 are both oriented forwards, so that the three powerlines 41 may not be twisted, whereby it is possible to make the wiringspace to be compact.

<Advantage of Electric Power Tool 10 of the Present Invention>

As shown in FIG. 1, in the electric power tool 10 of this embodiment,the switching elements 44 are arranged inside the grip portion 15, andare spaced apart from the electronic circuit board 50 for the electroniccomponent for operating the switching elements 44. Thus, the heat of theswitching elements 44 is not easily conducted to the microprocessor orthe like (electronic component) of the control circuit portion 46,thereby reducing the heat protection measures for the electroniccomponent.

Further, since the switching elements 44 are arranged inside the gripportion 15, there is no need for providing a space for the switchingelements 44 behind the DC brushless motor 20, so that the entire lengthof the electric power tool 10 may not increase.

Further, both end edges in the width direction of the power circuitboard 60 are supported by the inner wall surface of the grip portion 15,so that the contact area between the power circuit board 60 and the gripportion 15 is reduced, whereby the heat of the switching elements 44 isnot easily conducted to the grip portion 15.

Further, the board surface of the power circuit board 60 is orientedsubstantially in the same direction as the board surface of the motorboard 33 attached to the end surface of the brushless motor 20, so thattwisting is not easily generated in the three power lines 41 connectingthe power circuit board 60 (the switching elements 44) and the motorboard 33 (the DC brushless motor 20), making it possible to make thewiring space to be compact.

Further, the switching elements 44 are covered with the heatsink 65(heat radiation material) formed of aluminum alloy, so that theswitching elements 44 are not heated at high temperatures, whereby theheat of the switching elements 44 is not easily conducted to the gripportion 15.

<Modification Examples>

Here, it should be noted that the present invention is not restricted tothe above embodiment but allows modifications without departing from thescope of the invention. For example, in the embodiment described above,the switching elements 44 are covered with the heatsink 65 formed ofaluminum alloy, but it is also possible to cover the inner wall surfaceof the grip portion 15 with a heat insulating material instead ofproviding the heatsink 65 mentioned above. Further, it is also possibleto cover the inner wall surface of the grip portion 15 with a heatinsulating material, with the switching elements 44 being covered withthe heatsink 65 formed of aluminum alloy. Further, instead of coveringthem with the heatsink 65, it is also possible to cover the switchingelements 44 with a heat insulating material.

Further, in the embodiment described above, three switching elements 44are mounted to each of the board front surface and the board rearsurface of the power circuit board 60, and it is also possible toprepare two power circuit boards, three switching elements 44 beingmounted to each power circuit board. This makes it possible to improvethe cooling efficiency of the switching elements 44.

Further, an impact driver is shown as the electric power tool 10 in thisembodiment, and the present invention is also applicable to electricpower tools other than the impact driver described above.

EXPLANATION OF SYMBOLS

-   10 . . . electric power tool-   . . . 12 housing main body portion-   15 . . . grip portion-   15 h . . . handle portion-   16 . . . battery pack connection portion-   20 DC . . . brushless motor-   33 . . . motor board-   40 . . . drive circuit-   44 . . . switching element-   46 . . . control circuit portion-   50 . . . electronic circuit board-   60 . . . power circuit board-   65 . . . heatsink

1. An electric power tool, comprising: a brushless motor; a housing thathouses the brushless motor; a power circuit board that is housed in thehousing, wherein a first switching element is mounted on a first surfaceof the power circuit board and; wherein a second switching element ismounted on a second surface of the power circuit board.
 2. The electricpower tool according to claim 1, wherein the brushless motor iselectrically connected to the power circuit via three power lines suchthat twisting is not easily generated in the three power lines.
 3. Anelectric power tool, comprising: a motor; a housing that houses themotor; a circuit board that is housed in the housing, wherein a firstswitching element is mounted on a first surface of the circuit board;and wherein a second switching element is mounted on a second surface ofthe circuit board.
 4. The electric power tool according to claim 3,wherein the housing includes a housing main body portion that houses themotor and a grip portion that is coupled to the housing main bodyportion; and wherein the circuit board is disposed inside the gripportion and extends in a substantially vertical direction.
 5. Theelectric power tool according to claim 4, wherein a trigger type switchlever is provided in the grip portion; and wherein the circuit board isdisposed below the trigger type switch lever.
 6. An electric power tool,comprising: a motor; a housing that houses the motor; and a circuitboard that is housed in the housing, wherein a chuck is disposed on afront side of the housing; and wherein a first switching element ismounted on a front surface of the circuit board.
 7. The electric powertool according to claim 6, wherein a second switching element is mountedon a rear surface of the circuit board.